I'm not Keith, but from what I've read about such systems, this isn't a concern: when they hit the Earth's surface, the microwave beam is very large so it wouldn't have a fatal effect on anyone or anything that happened to cross through it, though it might warm you up a bit. Also, the frequency is pretty important; microwave ovens work because they're tuned to the resonant frequency of water, which most of our food is largely composed of, so it excites the water molecules and makes them heat up. If the be
Yes, very low energy per given area can ensure safety. But that means absolutely huge receivers are required to get a useful power level.
To receive the kind of power levels we're talking about efficiently, you're going to need pretty damned big receivers. Luckily, they don't have to be large single physical structures - you'll have a rectenna array rather than one big one.
So do solar panels. The difference is a rectenna array generates 300 W/m^2 for 24 hours a day, while solar panels generate about 200 W/m^2 from 4-6 hours a day in most decent locations. In crappy locations for solar (Seattle, Germany), the energy per land area is *way* higher for space beamed power.
' a rectenna array generates 300 W/m^2 for 24 hours a day
That is possible on the high end, but the topic of this thread was doing so with safe energy levels, and to be safe you need to be a lot closer to the 20 W/M^2 range. You can have a setup with higher levels in the center and lower at the edges of the beam, but when beaming from such a great distance it is difficult to manage such an intensity distribution.
For even 80 W/M^2 average, it would take a receiver surface area of about 3 square miles to produce 600 MW ( the size of a medium fossil plant, just fo
UV radiation is the component of sunlight that burns, it is only a slice of the spectrum. That part of the spectrum is not 200 W/m2.
Microwaves interact differently with the human body than UV radiation, so the comparison would not necessarily be telling. My quick searches showed safe levels need to be in the range I specified, I'll admit I don't know the science behind them.
Standing inside the fence of a rectenna array makes as much sense as going inside the furnace of a coal power plant. In other words, no sense at all.
300W/m^2 is the average intensity on the receiving antenna elements. The intensity outside the fence is much much lower. There's a buffer zone between the edge of the antenna and the fence.
Standing inside the fence of a rectenna array makes as much sense as going inside the furnace of a coal power plant. In other words, no sense at all.
300W/m^2 is the average intensity on the receiving antenna elements. The intensity outside the fence is much much lower. There's a buffer zone between the edge of the antenna and the fence.
That is not the configuration that most articles describe, where the antenna covers the full range down to safe levels. And it makes no sense because if you don't you are wasting a lot of energy falling on what is now a unusable zone outside the receiver, not to mention still taking up all that area which was part of the original point.
These space to earth systems are still a paper exercise. To state that "300W/m^2 is the average intensity on the receiving antenna elements." is not based on anything proven nor shown to be practical when controlling a beam over such a huge distance but still keeping the spread at a minimum. It may be possible. IF so, there is still a list of issues that comes to play when moving to higher energy levels, including significant EMI/RFI impacts. There is consideration of birds and insect flying overhead. etc.
' a rectenna array generates 300 W/m^2 for 24 hours a day
That is possible on the high end, but
Not even possible on the high end. The diffraction-limited beam spread means that you can't focus the beam to a tight spot, without making the space transmitter correspondingly larger. The Glaser sizing of a kilometer-scale transmitter in space beaming to a ten-kilometer scale spot on the ground wasn't picked at random; those are the sizes you need. And the keep-out zone around the ground receiver is much larger; due to the diffraction wings.
Shorter wavelengths make things better... but if you go too sho
The universe seems neither benign nor hostile, merely indifferent.
-- Sagan
Microwaving power to Earth from space (Score:1)
Re: (Score:4, Informative)
I'm not Keith, but from what I've read about such systems, this isn't a concern: when they hit the Earth's surface, the microwave beam is very large so it wouldn't have a fatal effect on anyone or anything that happened to cross through it, though it might warm you up a bit. Also, the frequency is pretty important; microwave ovens work because they're tuned to the resonant frequency of water, which most of our food is largely composed of, so it excites the water molecules and makes them heat up. If the be
Re: (Score:3)
Re: (Score:2)
Yes, very low energy per given area can ensure safety. But that means absolutely huge receivers are required to get a useful power level.
To receive the kind of power levels we're talking about efficiently, you're going to need pretty damned big receivers. Luckily, they don't have to be large single physical structures - you'll have a rectenna array rather than one big one.
Re: (Score:2)
Re: (Score:2)
So do solar panels. The difference is a rectenna array generates 300 W/m^2 for 24 hours a day, while solar panels generate about 200 W/m^2 from 4-6 hours a day in most decent locations. In crappy locations for solar (Seattle, Germany), the energy per land area is *way* higher for space beamed power.
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' a rectenna array generates 300 W/m^2 for 24 hours a day
That is possible on the high end, but the topic of this thread was doing so with safe energy levels, and to be safe you need to be a lot closer to the 20 W/M^2 range. You can have a setup with higher levels in the center and lower at the edges of the beam, but when beaming from such a great distance it is difficult to manage such an intensity distribution.
For even 80 W/M^2 average, it would take a receiver surface area of about 3 square miles to produce 600 MW ( the size of a medium fossil plant, just fo
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Why do you need 20W/m^2 for safety? The sun beams 200W/m^2 on sunny days and the worst damage it does is sunburn and deterioration of plastics.
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Microwaves interact differently with the human body than UV radiation, so the comparison would not necessarily be telling. My quick searches showed safe levels need to be in the range I specified, I'll admit I don't know the science behind them.
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Standing inside the fence of a rectenna array makes as much sense as going inside the furnace of a coal power plant. In other words, no sense at all.
300W/m^2 is the average intensity on the receiving antenna elements. The intensity outside the fence is much much lower. There's a buffer zone between the edge of the antenna and the fence.
Re:Microwaving power to Earth from space (Score:2)
Standing inside the fence of a rectenna array makes as much sense as going inside the furnace of a coal power plant. In other words, no sense at all.
300W/m^2 is the average intensity on the receiving antenna elements. The intensity outside the fence is much much lower. There's a buffer zone between the edge of the antenna and the fence.
That is not the configuration that most articles describe, where the antenna covers the full range down to safe levels. And it makes no sense because if you don't you are wasting a lot of energy falling on what is now a unusable zone outside the receiver, not to mention still taking up all that area which was part of the original point.
These space to earth systems are still a paper exercise. To state that "300W/m^2 is the average intensity on the receiving antenna elements." is not based on anything proven nor shown to be practical when controlling a beam over such a huge distance but still keeping the spread at a minimum. It may be possible. IF so, there is still a list of issues that comes to play when moving to higher energy levels, including significant EMI/RFI impacts. There is consideration of birds and insect flying overhead. etc.
Re: (Score:2)
' a rectenna array generates 300 W/m^2 for 24 hours a day
That is possible on the high end, but
Not even possible on the high end. The diffraction-limited beam spread means that you can't focus the beam to a tight spot, without making the space transmitter correspondingly larger. The Glaser sizing of a kilometer-scale transmitter in space beaming to a ten-kilometer scale spot on the ground wasn't picked at random; those are the sizes you need. And the keep-out zone around the ground receiver is much larger; due to the diffraction wings.
Shorter wavelengths make things better... but if you go too sho